Sedimentary response to Late Quaternary sea-level changes in the Romagna coastal plain (northern Italy)

Data from 17 continuously cored boreholes, 40-170 m deep, reveal the subsur face stratigraphy of the Romagna coastal plain. Sedimentological and microf aunal data allow the distinction of eight facies associations of Late Pleis tocene-Holocene age, including 18 lithofacies and 16 faunal associations. T en C-14 dates provide the basis to establish a sequence stratigraphic frame work for the succession corresponding to the upper part 35 ky BP of the las t glacioeustatic cycle. The eight facies associations can be grouped into l owstand, transgressive and highstand systems tracts. The upper part of the lowstand systems tract consists of alluvial plain deposits. These accumulat ed during the Late Pleistocene when the shoreline was approximate to 250 km south of its present-day position. A pronounced stratigraphic hiatus (betw een 25 and 8.8 ky BP) is invariably recorded at the upper boundary (transgr essive surface) of these Pleistocene, indurated and locally pedogenized all uvial deposits. The succeeding postglacial history is represented by a well developed transgressive-regressive cycle. Transgressive deposits, interpre ted to reflect the rapid landward migration of a barrier-lagoon system, inc lude two wedge-shaped, paralic and marine units. These thicken in opposite directions and are separated by a ravinement surface. Above the transgressi ve deposits, the maximum flooding surface (MFS) marks the change from a tra nsgressive barrier-lagoon complex to a prograding, wave-dominated delta sys tem (early Po delta). The MFS can be traced landwards, where it constitutes the base of lagoonal deposits. An aggradational to progradational stacking pattern of upper delta plain (marsh), lower delta plain (lagoon/bay), and delta front (beach ridge) deposits reflects the progressive increase in the sediment supply/ accommodation ratio during the following highstand. The a lluvial deposits capping the sequence accumulated by the 13th century AD, i n response to an avulsion event that caused abandonment of the former Po de lta lobe and the northward migration of the Po River towards its present po sition.